The genetic defect of cystic fibrosis (CF) remains to be discovered, and its identification would likely produce improvements in the diagnosis and treatment of this disorder. In a continued search for this defect, the content of neuraminic acid derivatives (collectively termed the "sialic acid" content) in normal and CF sera have been analyzed by an HPLC method (R. Boykins and T.-Y. Liu, J. Biochem. and Biophys. Methods 2, 71 (1980)), not previously used for this purpose. New and as yet unidentified components have emerged from chromatography of the sialic acid fraction of CF sera, in addition to the N-acetyl and N-glycolyl derivatives of neuraminic acid that appear in the serum of normal individuals. Investigation will be continued to improve upon the method of separation, to identify the new components, and to assess their relevance to the genetic defect.